1. Field of the Invention
The present invention relates to an ink, a method for improving intermittent discharge properties (hereinafter referred to as xe2x80x9cdischargeabilityxe2x80x9d) of an ink-jet recording apparatus, a method for recording an image, a recording unit, an ink cartridge, ink set, and an image recording apparatus.
2. Description of the Related Art
Known black inks for writing implements, e.g., fountain pens, felt-tip pens, and aqueous ballpoint pens, and for ink-jet recording devices contain carbon black as a black pigment and have a variety of compositions. These black inks enable high-density printing and have good printing fastness. In recent years, research and development on various compositions and physical properties of carbon black was performed with a view towards recording on a wide range of recording media, such as plain paper, e.g., copying paper which is typically used in offices, letter paper, bond paper, continuous business form paper, etc.
Japanese Patent Application Laid-Open No. 3-210373 discloses an ink containing acidic carbon black and an alkaline-soluble polymer. Japanese Patent Application Laid-Open No. 3-134073 discloses an ink-jet ink dispersion having good storage stability and superior dischargeability in bubble-jet recording apparatuses. Japanese Patent Application Laid-Open No. 8-3498 discloses an ink containing a self-dispersion-type carbon black, which can be dispersed into the ink without using any solvent, in order to solve technical problems of an ink containing carbon black and dispersant, that is, unstable dischargeability and low density of printed characters. PCT International Publication Number WO96/18695 (Japanese National Publication No. 10-510862) and U.S. Pat. No. 5,746,818 (corresponding to Japanese Patent Application Laid-Open No. 10-95941) disclose an ink-jet ink containing self-dispersion-type carbon black which can create high-quality images on recording media.
A known problem in conventional pigment-based inks is unstable dischargeability. For example, an ink is discharged from a given nozzle of an ink-jet recording head, the ink discharge is suspended for a predetermined time (for example, 20 seconds), and then the ink is discharged again (hereinafter, such discharge is referred to as xe2x80x9cintermittent dischargexe2x80x9d). In such a discharge mode, the ink may not be stably discharged, and thus the print quality may decrease in some cases (hereinafter, unstable dischargeability in intermittent discharge is referred to as xe2x80x9cpoor intermittent dischargeabilityxe2x80x9d).
When a black ink is used with inks of other colors (for example, at least one color ink selected from a magenta ink, a cyan ink, a yellow ink, a red ink, a green ink, and a blue ink) for color printing on a recording medium, these inks will blur and will be nonhomogenously mixed at boundaries between the black image sections and the color image on the recording medium in some cases, resulting in deterioration in image quality (hereinafter, referred to as xe2x80x9cbleedingxe2x80x9d). Several countermeasures for bleeding are reported. For example, Japanese Patent Application Laid-Open No. 55-65269 discloses addition of surfactant to an ink for improving ink penetrability into recording media, and Japanese Patent Application Laid-Open No. 55-66976 discloses use of volatile solvents in ink. In particular, high optical density (OD) and the formation of images having sharp edges are desirable qualities for black inks which are often used in the printing of characters, etc. The above-described ink showing improved penetration into recording media is believed to achieve both high optical density and the formation of images having sharp edges.
As quality in ink jet prints is becoming extremely high, expectations for the performance of black ink for ink-jet printing are rising. Regarding the black ink containing self-dispersion-type carbon black, however, enough knowledge for suppressing bleeding, or for achieving high OD, sharp edges, and satisfactory dischargeability in intermittent modes has not accumulated yet, and the behaviors of the ink during ink-jet recording are not fully known.
In view of the aforementioned technological background, the present inventors have conducted research on an ink containing a self-dispersion-type carbon black and discovered that intermittent dischargeability of the ink and ink fixation and image quality are greatly improved, when the amount of monovalent cations in an ink, whose penetration into plain paper is suppressed to a relatively low level, is controlled to be in a specific range.
Accordingly, an object of the present invention is to provide an ink containing a self-dispersion-type carbon black as a pigment and having superior ink-jet recording characteristics.
Another object of the present invention is to provide a method for improving intermittent dischargeability in ink-jet recording.
A further object of the present invention is to provide an ink set which can continuously produce images with suppressed bleeding.
Still another object of the present invention is to provide a method for recording images which can achieve high-quality printing with suppressed bleeding and satisfactory fixing and an image recording apparatus, and to provide an ink cartridge and a recording unit used therein.
According to a first aspect of the present invention, there is provided an ink comprising a coloring material and an aqueous medium, the coloring material comprising a self-dispersion-type carbon black in which at least one hydrophilic group is bonded to the surface of the carbon black directly or through another atomic group, wherein a Ka value of the ink determined by a Bristow""s test method is less than 1.5, and the total amount of monovalent cations in the ink is in a range of 0.05 to 1 mole/liter.
According to another aspect of the present invention, there is provided a method for improving intermittent dischargeability of an ink in an ink-jet recording apparatus having a means for applying energy to an ink in an ink channel of an ink-jet recording head so as to discharge the ink from an orifice, wherein the ink contains a self-dispersion-type carbon black and an aqueous medium, a Ka value of the ink determined by a Bristow""s test method is less than 1.5, and the total amount of monovalent cations in the ink is in a range of 0.05 to 1 mole/liter.
According to a further aspect of the present invention, there is provided a method for recording an image comprising a step of applying energy to an ink so as to discharge the ink from a recording head to adhere the ink to a recording medium, wherein the ink comprises a coloring material and an aqueous medium, the coloring material comprising a self-dispersion-type carbon black in which at least one hydrophilic group is bonded to the surface of the carbon black directly or through another atomic group, wherein a Ka value of the ink determined by a Bristow""s test method is less than 1.5, and the total amount of monovalent cations in the ink is in a range of 0.05 to 1 mole/liter.
According to a further aspect of the present invention, there is provided a recording unit comprising an ink reservoir for storing an ink and a recording head for ejecting the ink, wherein the ink contains a coloring material comprising a self-dispersion-type carbon black in which at least one hydrophilic group is bonded to the surface of the carbon black directly or through another atomic group, and an aqueous medium, has a Ka value determined by a Bristow""s test method of less than 1.5, and comprises a monovalent cation in an amount of from 0.05 to 1 mole/liter.
According to further aspect of the present invention, there is provided a cartridge comprising an ink reservoir for storing an ink, wherein the ink contains a coloring material comprising a self-dispersion-type carbon black in which at least one hydrophilic group is bonded to the surface of the carbon black directly or through another atomic group, and an aqueous medium, has a Ka value determined by a Bristow""s test method of less than 1.5, and comprises a monovalent cation in an amount of from 0.05 to 1 mole/liter.
According to a further aspect of the present invention, there is provided an apparatus for printing comprising a recording unit comprising an ink reservoir for storing an ink and a head for ejecting the ink, wherein the ink contains a coloring material comprising a self-dispersion-type carbon black in which at least one hydrophilic group is bonded to the surface of the carbon black directly or through another atomic group, and an aqueous medium, has a Ka value determined by a Bristow""s test method of less than 1.5, and comprises a monovalent cation in an amount of from 0.05 to 1 mole/liter.
According to a further aspect of the present invention, there is provided an apparatus for printing comprising an ink cartridge for storing an ink and a recording head for ejecting the ink, wherein the ink contains a coloring material comprising a self-dispersion-type carbon black in which at least one hydrophilic group is bonded to the surface of the carbon black directly or through another atomic group, and an aqueous medium, has a Ka value determined by a Bristow""s test method of less than 1.5, and comprises a monovalent cation in an amount of from 0.05 to 1 mole/liter.
According to a still further aspect of the present invention, there is provided an ink set comprising an ink containing a coloring material comprising a self-dispersion-type carbon black in which at least one hydrophilic group is bonded to the surface of the carbon black directly or through another atomic group, wherein a Ka value of the ink determined by a Bristow""s test method is less than 1.5, and the total amount of monovalent cations in the ink is in a range of 0.05 to 1 mole/liter, and at least one ink selected from the group containing of an ink consisting a coloring material for cyan, an ink containing a coloring material for magenta, an ink containing a coloring material for yellow, an ink containing a coloring material for red, an ink containing a coloring material for green, and an ink containing a coloring material for blue.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.